This invention relates to a control valve of an exhaust recirculation apparatus for an internal combustion engine of an automobile.
It is well known that part of the exhaust gas from an internal combustion engine is recirculated through the engine in order to restrict the production of nitrogen oxides (NOx). Usually, the quantity of exhaust gas recirculated is controlled by an exhaust gas recirculation valve (EGR valve) which controls the opening of an exhaust recirculation passage in accordance with the degree of vacuum being introduced into the EGR valve. The EGR valve is controlled by vacuum from various kinds of vacuum sources. For example, as described in U.S. Pat. No. 3,739,797, vacuum at a venturi portion of the carburetor is used, and U.S. Pat. No. 3,799,131 indicates in FIG. 7 thereof that the EGR valve is controlled by vacuum at a throttle portion of the carburetor, which vacuum is controlled by pressure in a zone defined in an exhaust recirculation passage by an orifice and the EGR valve.
There is a control valve for an exhaust recirculation apparatus which controls the EGR valve in accordance with vacuum from the throttle portion, which vacuum is controlled by the vacuum from the venturi portion and exhaust pressure in an exhaust inflow chamber corresponding to the above-mentioned zone just upstream of the EGR valve. The control valve has an exhaust pressure chamber with a diaphragm communicating with an exhaust inflow chamber defined in the exhaust recirculation by the EGR valve and an orifice disposed upstream of the EGR valve, a vacuum chamber defined by large and small diaphragms and communicating with a venturi portion of the carburetor, and a control chamber defined by the small diaphragm and a cover with an air hole communicating with the outside of the control chamber. The above-mentioned three diaphragms are mechanically connected to each other. In the control chamber there is disposed a vacuum passage which has an opening facing a seal member secured to the small diaphragm of the control chamber and which communicates with a throttle portion of the carburetor and the EGR valve. The control valve is further provided with a spring urging the diaphragms so that the seal member is parted from the opening of the vacuum passage.
Vacuum for controlling the EGR valve is controlled by adjusting the quantity of air flowing into the vacuum passage through the opening, and the quantity of air is controlled by the movement of the diaphragms according to the vacuum at the venturi portion and the exhaust pressure at the exhaust inflow chamber.
In the control device, in order to produce the driving force for the diaphragms in response to the vacuum induced into the vacuum chamber, the difference in area between the large diaphragm and the small diaphragm is used. Therefore, the control device, which employs two signals to control the vacuum for controlling the EGR valve in accordance with the vacuum from the venturi portion and the exhaust pressure in the exhaust inflow chamber, needs all three of the above-mentioned diaphragms, so that the movable portion of the control devices is very heavy. Because of the heavy portion, the control device has the inherent defect that its responsiveness is low. Further, because of the use of the three diaphragms, difficulty is encountered in assembling the control device.